1. Field of the Invention
The present invention relates to a method of cleaning surfaces made of glass, graphite, ceramics, polymeric and metallic materials, synthetic and vegetable fibres, e.g. fabrics, textiles or waste paper, in particular membrane surfaces, by detaching or dissolving organic and inorganic soilings by a simple flushing operation.
Deposits of organic and inorganic impurities are a constant problem in industry and the home. Thus, the deposits lead, for example, to a reduction in flow rate or even to blockages in pipes, to contaminations in reactors or soilings on objects of everyday use.
Glassware is particularly susceptible to soilings and is a particular problem in the domestic sector. In order to maintain the operation of equipment and materials and hygiene, the cleaning of surfaces is an important procedure in many fields.
Membranes, as a specific example of surfaces, are used in a variety of ways in industry and in the medical field. For their use to be economical, it is important to maintain a high flow rate. Deposits on the membrane surface partially block the membrane, resulting in a reduced and uneconomical permeate flow. Cleaning compositions can be used to largely remove the soilings and increase the flow rate again.
2. Description of the Related Art
The Aachen membrane colloquium, preprints page 41 (1991) reports on the use of various flushing chemicals; only alkaline formulations which contain, for example, EDTA, phosphates, anionic and nonionic surfactants and enzymes lead to adequate cleaning performances. Citric acid and peracetic acid do not exhibit an adequate action.
Permasep Engineering Manual, Bulletin 507, page 1-4 (1982) describes various cleaning compositions and cleaning procedures for cleaning membranes. The cleaning compositions proposed were frequently standard commercial cleaning compositions, which are a complex mixture of very many different active components.
Desalination, 77, 135-179 (1990) reports on flushing procedures for various applications of ultrafiltration, where purification is in some instances necessary after an operating period of just a few hours.
A list of cleaning compositions and their activity mechanisms is given in Desalination, 71, 325-335 (1989), and the need to use a variety of cleaning compositions in a certain sequence to achieve satisfactory cleaning performances is emphasized in particular.
The specialist journal Vom Wasser, 67, 59-68 (1986) reports on the optimization of flushing processes during water treatment using reverse osmosis plants, where the aim is to use chemically pure surfactants instead of formulated cleaning compositions. The investigations showed that a combination of EDTA and a formulated cleaning composition produced inferior performances than EDTA on its own.
EP 0 513 948 describes the cleaning of hard surfaces by a cleaning composition that is composed of a variety of components and inter alia comprises a complexing agent and an organic solvent.
EP 0 261 874 discloses a cleaning composition for hard surfaces which comprises EDTA and an alkanesulphonate. U.S. Pat. No. 4,808,328 likewise discloses cleaning compositions for hard surfaces which, in addition to EDTA, comprise an alkanesulphonate.
It is a common feature of all cleaning compositions and in particular all membrane cleaners which cover a broad field of use that they are composed of a complex mixture of many different cleaning chemicals and auxiliaries, and even that in most cases a flushing procedure with various cleaning compositions has to be carried out in a certain sequence for effective cleaning. In particular, most formulated membrane cleaners contain phosphates or phosphonates to improve the membrane cleaning performance.
Surprisingly, it has now been found that the use of a cleaning composition which comprises at least one component selected from the group consisting of
i) iminodisuccinic acid of the formula (I) 
xe2x80x83in which
R1, R2, R3 and R4 independently of one another are H, Li, Na, K, NH4, H3NCH2CH2OH, H2N(CH2CH2OH)2 or HN(CH2CH2OH)3,
R5 and R6 independently of one another are H or OH, and
R7 is H, CH2CH2OH, CH2CH2CH2OH, CH2CH(OH)CH3, CH2COOR8 or CH2CH2COOR8, where R8 independently of R1 has the scope of meanings of R1,
ii) polyamino acid or
iii) emulsifier,
xe2x80x83by a simple flushing operation (no procedure with various cleaners in sequence) achieves significantly better cleaning performances on surfaces, in particular membrane surfaces, than does the use of cleaners recommended in the literature. In addition, better cleaning performances are also achieved than when phosphate- and phosphonate-containing cleaners are used.
The invention relates to a method of cleaning surfaces made of glass, graphite, ceramics, polymeric and metallic materials, synthetic and vegetable fibres, and membranes by detaching or dissolving organic or inorganic soilings or a mixture of the two by a simple flushing operation with a solution of a cleaning composition at, in particular, 10-100xc2x0 C. and a pH of in particular 3-13, which is characterized in that the cleaning composition used is at least one component selected from the group consisting of
i) iminodisuccinic acid of the formula (I) 
xe2x80x83in which
R1, R2, R3 and R4 independently of one another are H, Li, Na, K, NH4, H3NCH2CH2OH, H2N(CH2CH2OH)2 or HN(CH2CH2OH)3,
R5 and R6 independently of one another are H or OH, and
R7 is H, CH2CH2OH, CH2CH2CH2OH, CH2CH(OH)CH3, CH2COOR8 or CH2CH2COOR8, where R8 independently of R1 has the scope of meanings of R1,
ii) polyamino acid or
iii) emulsifier,
xe2x80x83comprises and the solvent used is water or a mixture of water and a C1-C4-alcohol or a C3-C4-ketone.
The invention further relates to a composition for cleaning surfaces made of glass, graphite, ceramics, polymeric and metallic materials, synthetic and vegetable fibres and membranes, based on at least one component selected from the group consisting of
i) iminodisuccinic acid of the formula (I) 
xe2x80x83in which
R1, R2, R3 and R4 independently of one another are H, Li, Na, K, NH4, H3NCH2CH2OH, H2N(CH2CH2OH)2 or HN(CH2CH2OH)3,
R5 and R6 independently of one another are H or OH, and
R7 is H, CH2CH2OH, CH2CH2CH2OH, CH2CH(OH)CH3, CH2COOR8 or CH2CH2COOR8, where R8 independently of R1 has the scope of meanings of R1,
ii) polyamino acid or
iii) emulsifier
xe2x80x83and a solvent from the group consisting of water and a mixture of water and a C1-C4-alcohol or a C3-C4-ketone, where the solvent constitutes in particular 40-99.9% by weight, preferably 50-99% by weight, particularly preferably 60-90% by weight of the total composition.
The emulsifiers to be used according to the invention are preferably C8-C25-alkanesulphonates, particularly preferably C10-C20-alkanesulphonates, very particularly preferably C12-C18-alkanesulphonates. It is also preferable to use linear alkanesulphonates.
The iminodisuccinic acids of the formula (I) to be used according to the invention are used in aqueous solution.
Preferably, R6 is H, and particularly preferably R5 and R6 are H. In a likewise preferred manner, R7 is H. In a further preferred manner R5, R6 and R7 are H, so that (I) represents the unsubstituted iminodisuccinic acid (IDS) and its salts of the above-described type.
In a further preferred manner, the radicals R11, R12, R13 and R14 appear in the position of R1, R2, R3 and R4 and have the meaning H, Na, K, NH4 or H3NCH2CH2OH.
The iminodisuccinic acids of the formula (I) used according to the invention are in pure form or are combined with small amounts of secondary components from the preparation of (I), such as maleic acid, fumaric acid, aspartic acid, malic acid, asparagine, tartaric acid, hydroxyaspartic acid, condensates of aspartic acid etc. or their salts containing the above mentioned cations R1 to R4. The secondary components are present in the mixture in an amount of at most 35% by weight, preferably 30% by weight and particularly preferably 25% by weight; the remainder to 100% by weight is (I).
(I) is prepared by known methods in aqueous medium, for example from maleic anhydride, maleic acid or epoxysuccinic acid and ammonia or aspartic acid. Methods of this type are described, for example, in GB 1 306 331, SU 0 639 863, JP 6/329 607, JP 6/330 020 and DE 37 39 610.
The polyamino acids according to the invention are, for example, homo- and copolymers of lysine, glutamic acid, alanine and aspartic acid, and protein hydrolysates.
Preference is given to using polyaspartic acids or polymers with repeat succinyl units, which can either be prepared from aspartic acid or from maleic anhydride, its derivatives and ammonia.
In a preferred embodiment, the polyamino acids to be used according to the invention are polymers with repeat succinyl units which have at least one of the following repeat structural units: 
where the following statements apply:
R20 is H or is a cation, in particular alkali metal, ammonium, independently of one another where two or more are present,
n, m, o is 0 or an integer from 1 to 300,
p, q is 0 or an integer from 1 to 10,
r is 0 or an integer 1 or 2,
s is 0 or an integer from 1 to 10, and
n+m+o+p+q is xe2x89xa6300, where the indices n, m, o, p, q, r and s indicate how many units are present in the polymer, optionally in random distribution.
The polymers to be used according to the invention are taken to mean the corresponding free acids, their salts and also derivatives of the acids, in particular anhydrides.
In a particularly preferred embodiment, the repeat unit B1 is present, based on the total of units B1 and A1, to at least 50%, in particular to at least 70%.
The average molecular weight (MW) can fluctuate within a wide range, it being possible to use polyaspartic acids having molecular weights between 500 and 100,000 g/mol, but preference is given to from 1000 to 50,000 g/mol or, even better 1000 to 30,000 g/mol.
The molecular weight is determined using gel permeation chromatography (GPC) in LiChrospher diol acids (Merck) and using phosphate buffer (pH=7) as eluent solution. Calibration is best carried out using pure polyaspartic acid, e.g. Sigma, the molecular weight of which has been determined by an absolute measuring method, for example LALLS.
The polymers with repeat succinyl units to be used according to the invention are, in a preferred embodiment, essentially polyaspartic acids. The polymers can be prepared by known processes, for example in accordance with U.S. Pat. No. 4,839,461, U.S. Pat. No. 5,371,180, U.S. Pat. No. 5,288,783, J. Org. Chem., 24, p 1662-1666 (1959) and J. Org. Chem., 26, 1084 (1961).
The emulsifiers, iminocarboxylic acids and polyamino acids can be used alone or as mixtures. The mixture proportions (proportions by mass) of emulsifier, preferably C8-C25-alkanesulphonate, and iminocarboxylic acid or polyamino acid are in the range from 99:1 to 1:99, preferably from 20:80 to 80:20, particularly preferably from 40:60 to 60:40.
The mixing proportions of iminocarboxylic acid and polyamino acids are likewise in the range from 99:1 to 1:99, preferably from 20:80 to 80:20, particularly preferably from 40:60 to 60:40.
The cleaning composition concentrates according to the invention are used with a water content of from 99.9% by weight to 40% by weight, preferably from 95% by weight to 50% by weight, particularly preferably from 95% by weight to 60% by weight.
The cleaning compositions according to the invention are used at a pH of 3-13, preferably 4-12, particularly preferably 4.5-11.5, and at temperatures of 10-100xc2x0 C., preferably 15-85xc2x0 C.
The cleaning compositions according to the invention are used for cleaning surfaces made of glass, graphite, ceramics, polymeric and metallic materials, synthetic and vegetable fibres, e.g. fabrics, textiles or waste paper, in particular for cleaning membrane surfaces.
Membranes which are cleaned according to the invention are those which are preferably used in pressure permeation techniques. The membranes can be made of the following materials: cellulose esters, such as, for example, cellulose acetate, cellulose acetopropionate, cellulose acetobutyrate, polyolefins, such as polyethylene or rpolypropylene, copolymers of ethylene and C3-C8-olefins, polyimides, polyamides, polyphenylenesulphones, polyphenylene ethers, polyphenylenesulphonic esters, polyphenylene ether esters, ceramics, SiO2, carbon, polypiperazinamide, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polysulphone.
The membrane to be cleaned or the membrane module to be cleaned is treated with an aqueous, aqueous-alcoholic, aqueous-ketonic or aqueous-alcoholic-ketonic solution of the emulsifier, the iminocarboxylic acid, the polyamino acid or a mixture thereof, optionally with addition of standard commercial cleaning composition enzymes, such as, for example, proteases, lipases or amylases, in a manner which involves pumping such a solution over the membrane surface or through the membrane module. A suitable alcohol is C1-C4-alcohol, such as methanol, ethanol, propanol, i-propanol, butanol, i-butanol, preferably methanol, ethanol, i-propanol. A suitable ketone is acetone (C3) or methyl ethyl ketone (C4). Of these organic solvents, alcohols are preferred. The duration of the cleaning treatment is obviously dependent, in a manner familiar to the person skilled in the art, on the degree of soiling, on the intensity of the recirculation, on the concentration of the cleaning solution and, where present, on the said ingredients and also on the temperature. The extent of cleaning can be controlled by determining the flow rate through the membrane.
The cleaning composition according to the invention is prepared by simply dissolving the emulsifier and/or the iminodisuccinic acid of the formula (I) and/or the polyamino acid and optionally the alkali carrier or the enzyme or a plurality of such substances in water, a water/alcohol mixture, a water/ketone mixture or a water/alcohol/ketone mixture in the stated amounts and ratios. For storage or for dispatch purposes, a mixture of dry substances, for example flake material from a drying roller or spray-dry granules, can be prepared. Where liquid substances are used, for example highly concentrated alkali metal hydroxide solution or ethanolamine, a 10 to 60% strength by weight solution, for example, can be used for storage and dispatch.
In addition, the cleaning solution according to the invention can comprise other components, such as, for example, enzymes, alcohols, solubility promoters and auxiliaries and fragrances.
The cleaning performance of the cleaning compositions according to the invention may be demonstrated by the following examples: